1. Field of the Invention
This invention relates to a zinc galvanizing method for a single surface of a metal tube, particularly to one provided with various methods for option by users, possible to reduce subsequent expenditure required for maintaining the metal tube.
2. Description of the Prior Art
Nowadays metal tubes are indispensable for industries, such as for chemical factories, accommodations located near seaside or very humid locations where corrosion is very prevalent. It is conventional that metal tubes are galvanized with zinc, as shown in FIG. 1, and one of the zinc galvanized metal tubes has the inner and the outer surface 120 and 121 of a metal tube 1 galvanized, and another is one having both the inner and the outer surface 120 and 121 not galvanized. So there is no option for using a metal tube with only one surface, the inner or the outer, galvanized. For example, if a liquid or gas to flow through a metal tube can give rise to a chemical reaction with a zinc galvanized layer, the metal tube galvanized on both the inner and the outer surface is impossible to be used, only the metal tube with no galvanization is possible. But these kind of metal tubes should be sprayed with or painted with an anti-corrosion substance to prevent them from corroding.